This is simply poor behaviour on the part of your stepchildren.
My ex husband left me to marry another woman . Any gifts to my children from them both were acknowledged and thanked- for, and this is now continued to the grandchildren.
I do not see this as disrespectful to me, rather that it shows that I have raised them to be courteous and responsible people - so to my credit, then !
Definitely donations to charity this year.
My fridge abounds with magnets telling of my children, as gifts to me, purchasing schoolbooks, a kit for a midwife, a goat ( of course) and so on. It's a very proud fridge..